A steam generator is configured in such a way that a water level detection sensor detecting the level of water is installed in a steam tank which helps generate and store steam by boiling water using various energy source (heater, waste heat, etc.). When the water level lowers and the water level in the steam tank reaches a set minimum water level, the water level detection sensor detects such state, and a water supply control valve installed at a water supply tube automatically opens, so water can be supplied to the steam tank.
The above mentioned conventional steam generator needs an additional electric motor pump so as to supply new water to the steam tank unless water is supplied with a natural pressure based on an elevation difference between upper and lower positions because the water supply tank is provided at the top of the steam tank.
Since the interior of the steam tank maintains a high pressure itself, even when the water supply tank is provided at the top, water supply is not reliably performed. So as to overcome the above mentioned problems, it needs to install a motor pump with a large capacity, which is costly in installing related facilities, and it entails more electric power for the sake of a start and operations of a motor pump, so it is hard to obtain a high energy efficiency and operation performance, and the maintenance of such facilities is disadvantageously costly.
Therefore, it urgently needs to develop a technology of generating the optimum vacuum pressure in the interior of the pressurization water supply tank using a vapor pressure and of reliably supplying water to the pressurization water supply tank with a strong suction force generated by the vacuum pressure.